The present invention generally relates to golf balls, and more particularly to a golf ball having a cover which includes at least three layers.
Golf balls traditionally have been categorized in three different groups, namely as one-piece, two-piece and three-piece balls. Conventional two-piece golf balls include a solid resilient core having a cover of a different type of material molded thereon. Three-piece golf balls traditionally have included a liquid or solid center, elastomeric winding around the center, and a molded cover. Solid cores of both two and three-piece balls often are made of polybutadiene and the molded covers generally are made of natural balata, synthetic balata, or ionomeric resins.
Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability and flight characteristics, various Monomeric resins sold by E.I. DuPont de Nemours and Company under the trademark xe2x80x9cSurlyn(copyright)xe2x80x9d and by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademark xe2x80x9cEscor(copyright)xe2x80x9d and the trade name xe2x80x9clotekxe2x80x9d, have become the materials of choice for the construction of golf ball covers over the traditional xe2x80x9cbalataxe2x80x9d (transpolyisoprene, natural or synthetic) rubbers. The softer balata covers, although exhibiting enhanced playability properties, lack the durability (cut and abrasion resistance, fatigue endurance, etc.) properties required for repetitive play.
Ionomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid or maleic acid. Metal ions, such as sodium or zinc, are used to neutralize some portion of the acidic group in the copolymer, resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e., durability, etc., for golf ball cover construction over balata.
While there are currently more than fifty (50) commercial grades of ionomers available from Exxon and DuPont, with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (i.e., relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients such as reinforcement agents, etc., a great deal of research continues in order to develop a golf ball cover composition exhibiting the desired combination of playability properties.
Golf balls are typically described in terms of their size, weight, composition, dimple pattern, compression, hardness, durability, spin rate, and coefficient of restitution (COR). One way to measure the COR of a golf ball is to propel the ball at a given speed against a hard massive surface, and to measure its incoming and outgoing velocity. The COR is the ratio of the outgoing velocity to the incoming velocity and is expressed as a decimal between zero and one.
There is no United States Golf Association limit on the COR of a golf ball but the initial velocity of the golf ball must not exceed 250xc2x15 ft/second. As a result, the industry goal for initial velocity is 255 ft/second, and the industry strives to maximize the COR without violating this limit.
U.S. Pat. Nos. 4,431,193 and 4,919,434 disclose golf balls with multi-layer covers. U.S. Pat. No. 4,431,193 discloses a multi-layer ball with a hard inner cover layer and a soft outer cover layer. U.S. Pat. No. 4,919,434 discloses a golf ball with a 0.4-2.2 mm thick cover made from two thermoplastic cover layers. U.S. Pat. No. 5,273,286 discloses a golf ball with a multi-layer core. The golf ball disclosed therein has an inner core, a shell surrounding the inner core, an outer core, and a cover.
An object of the invention is to provide a golf ball for a low handicap player which has a favorable combination of spin and feel.
Another object of the invention is to provide a golf ball for a high handicap player which-has a favorable combination of spin and feel.
A further object of the invention is to provide a method of making multi-layer golf balls in which the characteristics-of spin and feel can be carefully controlled to result in a desired combination of these properties.
Other objects of the invention will be in part obvious and in part pointed out more in detail hereinafter.
A preferred form of the invention is a golf ball comprising a solid or wound core, an inner cover layer formed around the core, an intermediate cover layer formed around the inner cover layer, and an outer cover layer formed around the intermediate cover layer, each cover layer having a different. Shore D hardness than each adjacent cover layer. The outer cover layer preferably comprises ionomer.
The invention in another preferred form is a golf ball comprising a solid or wound core, an inner cover layer formed around the core, the inner cover layer having a Shore D hardness of at least 62, preferably in the range of 62-90, an intermediate cover layer formed around the inner cover layer, and an outer cover layer formed around the intermediate cover layer, each cover layer having a different Shore D hardness than each adjacent cover layer.
In a particularly preferred form of the invention, the intermediate cover layer is softer than the inner and outer cover layers. In another embodiment, the intermediate cover layer is harder than the outer cover layer and softer than the inner cover layer. In yet another embodiment, the intermediate cover layer is softer than the outer cover layer and harder than the inner cover layer. In a fourth embodiment, the intermediate cover layer is harder than the inner and outer cover layers. Each of the inner, intermediate and outer cover layers preferably has a thickness of 0.01-0.20 inches,-and more preferably 0.025-0.15 inches.
The outer cover layer preferably comprises ionomer. The inner and intermediate cover layers preferably are thermoplastic. In particularly preferred forms of the invention, the inner cover layer and/or intermediate cover layer also comprise ionomer.
The inner, intermediate and/or outer cover layers may contain at least one part by weight of a filler based upon 100 parts of resin composition. If filler is used, it preferably is included in an amount of at least 5 parts by weight based upon 100 parts by weight of resin composition. The filler preferably is selected from the group consisting of precipitated hydrated silica, clay, talc, asbestos, glass, aramid fibers, mica, calcium metasilicate, barium sulfate, zinc sulfide, lithopone, silicon carbide, silicates, diatomaceous earth, carbonates, metals, metal alloys, metal oxides, metal stearates, particulate carbonaceous materials, cotton flock, cellulose flock, leather fiber, micro balloons and combinations thereof.
In one form of the invention, at least one of the inner cover layer and intermediate cover layer comprises a non-ionomeric polyolefin material. This material preferably includes at least one member selected from the group consisting of low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, rubber-toughened olefin polymers, acid copolymers which do not become part of an ionomeric copolymer, plastomers including metallocene catalyzed polyolefins, flexomers, styrene/butadiene/styrene, block copolymers, styrene/ethylene-butylene/styrene block copolymers, dynamically vulcanized elastomers, ethylene vinyl acetates, ethylene methyl acrylates, polyvinyl chloride resins, polyamides, amide-ester elastomers, graft copolymers of ionomer and polyamide, crosslinked transpolyisoprene blends, thermoplastic block polyesters, thermoplastic polyurethanes and thermosetting polyurethanes.
A further preferred form of the invention is a golf ball comprising a solid core, an inner cover layer, an intermediate cover layer and an outer cover layer. The inner cover layer comprises at least one member selected from the group consisting of ionomers, thermoplastic elastomers and non-ionomeric polyolefins. The intermediate cover layer comprises at least one member selected from the group consisting of ionomers, thermoplastic elastomers and non-ionomeric polyolefins. The outer cover layer comprises at least one member selected from the group consisting of ionomers, thermoplastic elastomers and non-ionomeric polyolefins and preferably comprises an ionomer. Each of the inner cover layer, the intermediate cover layer and the outer cover layer is a separate and distinct layer.
In the golf ball of the invention,.at least one of the inner cover layer and the intermediate cover layer can be foamed. Furthermore, the outer cover layer can be foamed as long as molding does not result in unacceptable surface imperfections on the ball.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others and the article possessing the features, properties, and the relation of elements exemplified in the following detailed disclosure.